1. Technical Field
As described above, according to the optical disc of the present embodiment, since the phase difference of the grooves on the both sides of the land is set to 90 degrees or less, the maximum variation of the track width of the land can be decreased to approximately 70% of the case of the optical disc having the phase difference of the adjacent wobbles which is 90 degrees.
2. Related Art
In a field of video technology, optical discs such as DVD, BD (Blu-ray (registered trademark) Disc), and the like are well-known. These optical discs are used as media for recording video data and also used as external storage media for personal computers. As external storage media for personal computers, hard disks, flash memories, and the like are also used. Compared with such media, the optical disc media have advantages of long-life, high reliability, and no power necessary for retaining data. In view of the advantages, the optical disc media attract attention as archive media for storing important data, which is managed by data centers and the like. However, even an optical disc BD-XL which is one of the optical discs having the largest storage capacity, has a storage capacity of 128 GB per one disc. Therefore, a number of optical discs are required to store significantly large amount of data, and thus, a large space for storing such optical discs is required. Accordingly, it is required to further increase recording density of optical disc media (for example, JP 2004-265546 A).